A trial to characterize the immunogenicity of 2 different formulations of a vaccine from GSK Biologicals, including the following five antigens: diphtheria, tetanus, pertussis, hepatitis B and Haemophilus influenzae type b. A vaccine from Commonwealth Serum Laboratories (diphtheria, tetanus, pertussis) which is co-administered with Haemophilus influenzae type b vaccine will also be used as a comparator. Reactogenicity and safety of all vaccines will be assessed as well.